At present, an exhaust gas purification apparatus using DPF (Diesel Particulate Filter) has been put to practical use as an apparatus for collecting fine particles such as PM (Particulate matter) contained in exhaust gas. In such an exhaust gas purification apparatus, the fine particles such as PM, etc., are deposited on the DPF by use, and thus it is required to regenerate the DPF. As a method for regenerating the DPF, for example, a method of using a high frequency electromagnetic wave such as a microwave, etc., emitted from a microwave heating apparatus is disclosed (for example, Patent Document 1). Specifically, according to the disclosed method, the DPF is regenerated by irradiating the DPF with an electromagnetic wave such as a microwave, etc., to heat fine particles such as PM, etc., accumulated in the DPF and burn the fine particles.
[Patent Document 1] Japanese Laid-open Patent Publication No. 2006-140063
[Patent Document 2] Japanese Laid-open Patent Publication No. 2011-252387
[Patent Document 3] Japanese Laid-open Patent Publication No. 10-220219
[Patent Document 4] Japanese Laid-open Patent Publication No. 9-112249
In the exhaust gas purification apparatus described above, the regeneration of the DPF is carried out, after the fine particulates such as PM, etc., have been accumulated in the DPF to some extent, by irradiating the DPF with electromagnetic waves such as microwaves, etc., which causes the fine particulates such as PM, etc., to be heated and oxidized and decomposed. However, since the DPF is covered by a casing, it is unknown from the outside whether or not fine particles such as PM, etc., have been accumulated in the DPF.
For this reason, for example, a method of judging a regeneration timing of the DPF and performing the regeneration using a regeneration timing judgment map for estimating the regeneration timing based on a relationship between intensity of the microwave detected by a microwave sensor and an operation time of an internal combustion engine (For example, Patent Document 3). However, according to the method disclosed in Patent Document 3, since the regeneration timing of the DPF is estimated from the intensity of the microwave and the operation time of the internal combustion engine, the regeneration timing may not be correctly detected in some cases. If the regeneration timing of the DPF is not correctly detected, such problems that the microwave is radiated at an unnecessary timing, the DPF is not regenerated even after the fine particulates such as PM, etc., have been accumulated in the DPF, etc., occur. Further, according to the method disclosed in Patent Document 3, it is necessary to prepare the regeneration timing judgment map and the like, and it is necessary to memorize the regeneration timing judgment map and the like. Furthermore, according to the method disclosed in Patent Document 3, the control circuit for judging the regeneration timing also becomes complicated, and it takes time to implement the judgment, which leads to cost increase.